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Binary Interactions and
the Shaping of Planetary Nebulae
Philipp Podsiadlowski (Oxford)
• the majority of stars are in binary systems
• binary interactions affect the shaping of planetary
nebulae
• Question: are all/most asymmetric planetary neb-
ulae affected by binary interactions?
I. Physical Causes of Asymmetry
II. Review of Binary Interactions
III. The Role of Wide Binaries (Mira AB)
IV. Overall Assessment
The Origin of PN Asymmetries
• Shaping by the external medium
. interacting wind model (Kwok, Volk, Balick)
. due to asymmetric AGB wind (equatorially
enhanced)
. very successful in describing observed
morphologies
• Asymmetric ejection
. common-envelope (CE) ejection, binary merging
• The role of rotation (axi-symmetry!)
. ‘true’ single stars are slowly rotating in the AGB
phase (angular-momentum conservation!),
including their cores (slow rotation of young white
dwarfs)
• Magnetic Fields
. strong required B fields require dynamo → rapid
rotation (CE phase, merger?)
• binary interactions are the most natural cause of the
observed asymmetries
Binary Interactions
• most stars are members of binary systems
• a large fraction are members of interacting
binaries
• rule of thumb: each decade of log P contains
10% of all stars (for P from 10−3− 107 yr)
→ 50 % of all stars are in binaries with
Porb < 100yr
• mass-ratio distribution:
. for massive stars: masses strongly correlated
. for low-mass stars: uncertain/controversial
(if masses correlated → more asymmetric PNe
for more massive stars)
• binary interactions
. common-envelope (CE) evolution
. stable Roche-lobe overflow
. binary mergers
. wind focusing
Common-Envelope (CE) Ejection
• at least 10 − 15% of PNe are ejected
common envelopes (Bond, De
Marco)
• most known post-CE binaries have
Porb ∼< 3d
• the real numbers could be much
larger (De Marco, Afsar & Bond,
Sorensen & Pollaco)
• binary population synthesis [BPS]:
(Han et al. 1995)
. 10 − 15% from FGB
. ∼ 5% from AGB
→ constrains CE ejection efficiency
He
MS
P = 0.1 − 10 daysorb
sdBM = 0.4 − 0.49 M
sun
Common−Envelope Channels CE only (mass ratio > 1.2 − 1.5)
unstable RLOF −−−> dynamical mass transfer
common−envelope phase
short−period sdB binary with MS companion
Stable Roche-Lobe Overflow
• a tidally locked, Roche-lobe filling
AGB star is rapidly rotating
vrot/vbreak = (1 + q)1/2(
R1
a
)3/2
(0.33 [q = 1], 0.41 [q = 0.2])
• many post-AGB stars are in circular
binaries with Porb > 100d (Van
Winckel)
but: evolution presently unclear (see
talk by Frankowski)
• quasi-dynamical mass transfer?
(PhP 1992)
• with or without temporary CE?
→ binary mass loss: yes; PN formation:
not necessarily (no dynamical
ejection or superwind phase!)
P = 10 − 500 daysorb
sdBM = 0.30 − 0.49 M
sun
(mass ratio < 1.2 − 1.5)
Stable RLOF Channel
stable RLOF (near tip of RGB)
wide sdB binary with MS/SG companion
Binary Mergers
• one of the most important, but not well studied
binary interactions
• BPS: ∼ 10% of all stars are expected to merge
with a companion star
• efficient conversion of orbital-angular momentum
to spin orbital-angular momentum
• if mergers occur early in the evolution →
subsequent spin-down just as for single stars
• need late mergers or
• late merger with a planet? (Livio, Soker)
(planetary systems common, enough angular
momentum to moderately spin up envelope →
elliptical PNe?)
Merger candidates: SN 1987A, FK Comae, V Hyd,
B[e] supergiants [R4], Sher 25, HD168625, ηCar,
V838 Mon.
The Triple-Ring Nebula around SN 1987A
SN 1987A: an anomalous supernova
• progenitor (SK −69◦202): blue
supergiant with recent
red-supergiant phase (104 yr)
• chemical anomalies
• the triple-ring nebula
. not a limb-brightened hourglass,
but physically distinct rings
. axi-symmetric, but highly
non-spherical
• supernova is at the centre, but outer
rings are slightly displaced
• dynamical age: ∼ 20,000yr
all anomalies linked to a single event a
few 104 yr ago, most likely the merger
of two massive stars
Formation of the Triple-Ring Nebula
(Morris and Podsiadlowski 2007)
• 3-dim SPH simulations
(GADGET; Springel)
• simulate mass ejection during
merger and subsequent
blue-supergiant phase
• angular momentum of orbit →
spin-up of envelope
→ flattened, disk-like envelope
• energy deposition in rapid
spiral-in phase (∼< 1/3Ebind)
→ partial envelope ejection → outer
rings, bipolar lobes
• equatorial mass shedding during
red-blue transition → inner ring
equatorial
mass shedding
blue supergiant wind
ejecta from merger
a.
b. c.
d.
unstable mass transfer
red−blue transition and
blue−supergiant wind
sweep−up of ejecta by
partial envelope ejectionspin up of common envelope
MS COCOMS
Gravitational Focusing
(Morris, Fabian, Pilyugin)
• companion gravitationally focuses wind from
AGB star
→ equatorially enhanced wind
• focusing fraction (Morris)
αf ≡Mfocus
Moutflow
= 0.8Vw
[
M2
a
]2 [
V2w + 0.9 M1+M2
a
]
−3/2
• requires fairly close companion
• BPS:
. strong focusing (αf > 0.5): ∼ 3%
. mild focusing (αf > 0.1): ∼ 10%
but: the case of Mira AB: gravitational focusing
even in fairly wide binaries
The Symbiotic Binary Mira AB
• wide binary (Porb ∼> 1000yr), consisting
of Mira A (Ppuls ' 330d) and an
accreting white dwarf
• M ∼ 10−7 M� yr−1
Recent Observations:
• soft X-rays (Chandra, Karovska et al.
2005) from both components (shocks in
the wind of Mira A and from accretion
disk)
• the envelope of Mira is resolved in
X-rays and the mid-IR (Marengo et al.
2001)
. the slow wind from Mira A fills its
Roche lobe (RRL ∼ 40AU)
. but: radius of Mira A: 1 – 2AU
• a new mode of mass transfer(?): wind
Roche-lobe overflow
• important implications for D-type
symbiotics
Mass Loss from Mira Variablesin Binaries (Mohamed, P.)
• large-amplitude Mira pulsations lift
matter of the atmosphere (but not to
escape speed)
• pumping mechanism → till gas
reaches low temperatures for dust
formation
• radiation pressure on dust accelerates
matter to escape speed
Mira variables in binaries
• if dust-formation radius (Rdust) is a
significant fraction of the Roche-lobe
radius (RRL)→ binary effects affect
the mass-loss geometry
• transition from
. spherical wind for Rdust � RRL
. disk-like outflow
. wind Roche-lobe overflow for
Rdust ∼ RRL
. unstable mass transfer? for
Rdust > RRL
• formation of circumbinary disk
possible plus bipolar component
from accreting source
NB: Application to WR binaries?
• where RRL less than the outer wind
acceleration radius (Grafener &
Hamann 2005)
Wind Roche-Lobe Overflow
• a new mass-transfer mode for wide bina-
ries
• high mass-transfer fraction (compared to
Bondi-Hoyle wind accretion) → more ef-
ficient accretion of s-process elements for
the formation of barium stars (without
circularization)
• accretion rate in the regime where WDs
can accrete? → increase the range for SN
Ia progenitors (but may not be efficient
enough)
• asymmetric system mass loss → forma-
tion of circumstellar disks and bipolar
outflows from accreting component (e.g.
OH231.8+4.2)
→ shaping of (proto-)planetary nebulae
. binaries with longer orbital periods
important
Case D Mass Transfer
• extension of case C mass transfer, but
potentially more important (possibly
larger orbital period range)
• also: massive, cool supergiants with
dynamically unstable envelopes (e.g.
Yoon & Langer)
• large mass loss just before the super-
nova?
• possible implications for Type II-L,
IIb supernovae (increases rate esti-
mates), SN 2002ic
• delays onset of dynamical mass trans-
fer
→ produces wider S-type symbi-
otic binaries (i.e. solve orbital pe-
riod problem)
→ solve the problem of black-hole
binaries with low-mass compan-
ions
Implications for PN Shaping
• even in fairly wide binaries, gravitational
focusing is important
• asymmetric system mass loss → formation of
circumstellar disks and bipolar outflows from
accreting component (e.g. OH231.8+4.2)
→ shaping of (proto-)planetary nebulae
• depends on vwind and vorb
• as star climbs AGB → Mira phase: expect
transition from spherical wind to equatorial wind
gravitational focusing is much more important
than previous estimates suggested
The Importance of Binary Interactions
• results from binary population synthesis (Han)
CE ejection 15− 20%
Binary mergers ∼ 10% −5% (early mergers)
+10%? (planet mergers)
Roche-lobe overflow ?
Gravitational focusing ∼ 10− 20% +20%? (Mira!)
35− 50% +25%
Discussion
• binary interactions likely to be the dominant
cause for asymmetric planetary nebulae
• probably all bipolar/butterfly PNe
• elliptical PNe: only need moderate asymmetry:
planets, early mergers, distant companions, single
stars
• Are all PNe caused by binary interactions (Iben,
Paczynski, De Marco)?
. Personal judgement: necessity of binarity is
unproven/unclear
. single stars should also be able to produce PNe